In a wireless communication system that performs transmission and reception using a micro-wave band or a millimeter-wave band, a band-pass filter is used to pass signals in a predetermined frequency band and to remove unnecessary frequency components. Patent Literature 1 discloses a technique relating to a band-pass filter capable of changing a pass band.
Specifically, Patent Literature 1 discloses that a semi-coaxial resonant element is arranged inside a cavity resonator, and a movable conductor is arranged in a space between a cover covering the cavity resonator and an open end of the resonant element, and resonance frequency of the cavity resonator is changed by moving the movable conductor. Patent Literature 1 further discloses that a similar movable conductor is arranged in a space between two cavity resonators, and a coupling coefficient between two cavity resonators is changed by moving the movable conductor to change a bandwidth of a pass band.